Ultrasonic bonding apparatuses designed to apply a pressure and ultrasonic vibration to work pieces, thereby to bond the work pieces together, has a distal-end tool, an ultrasonic horn, an ultrasonic transducer, and an ultrasonic oscillator. The distal-end tool applies vibration and pressure to the work pieces. The ultrasonic horn transmits vibration and pressure to the distal-end tool. The ultrasonic transducer mechanically vibrates the ultrasonic horn. The ultrasonic oscillator supplies drive power to the ultrasonic transducer.
In any ultrasonic bonding apparatus of this type, the ultrasonic oscillator undergoes a frequency-tracking control using a phase locked loop (PLL) oscillation circuit.